This proposal describes the career development plan for Dr. Pavan Auluck to transition to a successful independent physician-scientist. Dr. Auluck completed his clinical training in Anatomic Pathology and Neuropathology at the Massachusetts General Hospital, and is now engaged in a research fellowship mentored by Dr. Susan Lindquist at the Whitehead Institute for Biomedical Research. Dr. Auluck will receive additional guidance from Dr. Matthew Frosch, Director of Neuropathology Service, and Dr. David Louis, Chair of Pathology at the Massachusetts General Hospital. This grant will provide the protected time so that Dr. Auluck will gain expertise in new research techniques with formal coursework and numerous scientific seminars and meetings. The environment at both the Massachusetts General Hospital and Whitehead Institute provides the unique opportunity for Dr. Auluck to gain the training required in protein biology, chemical biology, and neurodegenerative diseases to conduct the proposed research and to proceed towards a successful academic career. The synucleinopathies, Parkinson disease and dementia with Lewy bodies, are second only to Alzheimer disease in frequency among the elderly. These diseases are characterized by neurodegeneration in the brainstem and cortex along with the deposition of -synuclein within neurons as compact aggregates known as Lewy bodies and neurites. While the causes of Parkinson disease and dementia with Lewy bodies remain enigmatic, familial forms of the diseases have yielded clues. Genetic mutations and abnormal folding of - synuclein are clearly linked to the pathogenesis of these diseases. Overexpression of wildtype and mutant - synuclein in the budding yeast, Saccharomyces cerevisiae, has revealed strong dose-dependence for - synuclein toxicity, just as in the human disorders. Forward genetic screens have revealed vesicle trafficking defects, proteosomal impairment and alterations in metal-ion homeostasis when -synuclein is expressed at intermediate levels. These core cellular pathways perturbed by -synuclein toxicity proved conserved from yeast to mammalian neurons. With higher expression levels of -synuclein, yeast cells also exhibit profound mitochondrial dysfunction. At the same time, -synuclein does not localize to the mitochondria. Instead, mitochondrial dysfunction appears to be the indirect consequence of other severe -synuclein-mediated cellular pathologies. This proposal describes aims to test the hypotheses that -synuclein induced ER-to-Golgi vesicle trafficking defects precede and cause mitochondrial dysfunction and that the retromer trafficking complex, which can associate with mitochondria in addition to mediating retrograde vesicle trafficking, is also disrupted by -synuclein overexpression. Also, chemical probes identified in small molecule screens for compounds that rescue both mitochondrial dysfunction and vesicle trafficking defects will be used to identify and dissect novel pathways linking these distinct -synuclein mediated cellular pathologies.